The invention relates to an apparatus for the temporary storage and controlled feeding of volatile fuel components contained in the head space of a fuel tank system into the intake tube of an internal combustion engine. A line provided between the head space and the induction tube contains an absorption element and can be shut off by a signal-actuated servo valve connected to the output from the absorption element. The servo valve has an admittance which is variable by a vacuum actuator and can be actuated by the signal from a diagnosis block which processes data relating to the state of operation of the internal combustion engine.
Such an apparatus is disclosed in DE-OS 3909887, which describes a method for checking the functionality of a tank venting valve by which the air charged with fuel vapors can be fed to the intake of an internal combustion engine. For the practice of this method, factors are measured at the tank venting valve, such as pressure, mass flow or volumetric flow of volatile fuel components through a line. Provision is made for sensors to precede as well as follow the tank venting valve (in the direction of movement of the volatile fuel components), each sensor carrying signals to a diagnosis block. The data entering the microprocessor are preferably processed by determining differences. Irregularities affecting the controllability of the tank venting valve are made visible in a display if they exceed an established tolerance.
However, it is to be noted that monitoring the controllability of the tank venting valve is made possible by means of a sensing system that is delicate as well as not very satisfactory from the economic point of view, which is used in addition to system components that already exist.
The invention is addressed to the problem of improving an apparatus of the kind described above so as not to use a high-cost and delicate sensing system, but to resort insofar as possible to available signals and to accomplish this by the simple modification of available system components, thus achieving considerable savings while improving performance.